1. Field of Invention
The invention relates to a display device and an electronic appliance, and more particularly to a display device in which pixels including electro-optical components are two-dimensionally (2D) arranged in the form of a matrix and an electronic appliance having the display device.
2. Description of the Related Art
Recently, in the field of display devices that perform image display, plane-type (flat panel type) display devices in which pixels (pixel circuits) are arranged in the form of a matrix have been rapidly spread. As a kind of plane type display device, there is a display device that uses a so-called current driving type electro-optical component, in which luminance is changed according to a current value that flows in the device, as a light-emitting device of a pixel. As a current driving type electro-optical component, an organic electroluminescence (EL) device is known, which has a phenomenon of emitting light when an electric field is applied to an organic thin film using EL that is an organic material.
An organic EL display device that uses organic EL devices as light-emitting devices of pixels has the following characteristics. That is, since the organic EL device can be driven by an applied voltage equal to or lower than 10V, it consumes little power. Since the organic EL device is a self-light emitting device, it has a high visual recognition of an image in comparison to a liquid crystal display, and since it does not require an illumination member such as a backlight or the like, it is easy to make it light-weight and ultra-thin. Also, since the response speed of the organic EL device is very high to the extent of several μs, no afterimage is generated when a moving image is displayed.
In the same manner as a liquid crystal display, an organic EL display device may adopt a simple (passive) matrix type and an active matrix type as its driving type. However, according to the simple matrix type display device, although it has a simple structure, the light-emitting term of the electro-optical components is decreased as the number of scanning lines (that is, the number of pixels) is increased, and thus it is difficult to realize a large-scale high-definition display device.
Because of this, the development of an active matrix type display device in which current flowing through electro-optical components is controlled by active elements installed in pixels such as the electro-optical components, for example, insulated gate field effect transistors, have been actively made. As the insulated gate field effect transistor, generally, a TFT (Thin Film Transistor) is used. According to the active matrix type display device, the electro-optical components continue light emission through a period of one display frame, and thus it is easy to realize a large-scale high-definition display device.
A pixel circuit that includes a current driving type electro-optical component, which is driven by the active matrix type, is provided with a driving circuit for driving the electro-optical component in addition to the electro-optical component. A pixel circuit is known, which is configured to have an organic EL device 21 that is a current driving type electro-optical component, a driving transistor 22 as a driving circuit, a write-in transistor 23, and a maintenance capacity 24 (for example, see JP-A-2008-310127).
JP-A-2008-310127 discloses that when a gate electrode of a driving transistor 22 is in a floating state, a gate potential Vg is changed in association with a source potential Vs of the driving transistor 22 to perform a so-called bootstrap operation (see Paragraph No. 0071 of JP-A-2008-310127). JP-A-2008-310127 also discloses that even if the I-V characteristic of the organic EL device 21 is time-dependently changed, the gate-source voltage Vgs of the driving transistor 22 is maintained constant, and thus light emitting luminance is maintained constant (see Paragraph No. 0093 of JP-A-2008-310127).